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Vancouver 2018

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Date of release: 26 April, 2010

Lifetime exposure to estrogen and obstructive coronary disease in women

Introduction

The length of estrogen exposure throughout a woman’s lifetime and the risk of coronary heart disease (CHD) have been previously investigated with conflicting results [1]. The premise is that decreased lifetime duration of estrogen exposure increases the incidence of CHD (atherosclerosis). The Framingham study has lent credence to this hypothesis since women with premature or early menopause (natural or surgical) had an increased risk of CHD compared to age-matched women with intact or normal ovarian function [2]. Surgical menopause, a bilateral oophorectomy, is associated with an early onset of CHD in women who did not use hormone therapy (HT) compared to those who used replacement estrogen [3-5]. These data favor the hypothesis that the lifetime duration of exposure to endogenous and exogenous estrogen reduces the incidence or risk of atherosclerosis. This hypothesis is modified by other factors in a woman’s life such as smoking, diet, exercise and, of course, concurrent medical disease such as hypertension or diabetes.

The current study by Merz and colleagues is an analysis of the data from the Women’s Ischemia Syndrome Evaluation (WISE). The population consisted of 646 postmenopausal women who had symptoms that required evaluation for obstructive coronary artery disease (CAD) using angiography. CAD was defined as > 70% luminal diameter stenosis in more than one major epicardial coronary artery. They also evaluated a threshold of > 50% stenosis as an alternative definition of obstructive CAD. An overall CAD severity score was assigned based on severity of stenosis, location of stenosis, and presence of partial or complete collaterals [1]. The authors used a questionnaire that captured menstrual history, pregnancy, hormonal contraception use and HT.

The duration of total estrogen exposure time (TET) was not related to the incidence or risk of CAD. Total estrogen exposure was the summation of the duration of estrogen exposure based on the normal menstrual cycles (menarche to menopause), plus premenopausal oral contraceptive use and pregnancy time. The authors then used sustained total estrogen exposure time (sTET), which is TET plus postmenopausal HT time, and found that there was a significant correlation, with a reduction in the occurrence of CAD. Postmenopausal HT in the highest tertile of sTET appeared to protect against CAD. Comparing across all tertiles of sTET, the women who never used HT had the highest prevalence and severity of CAD, followed by women with up to 5½ years of HT use, with the lowest prevalence and severity of CAD in the women using HT for more than 5½ years (p < 0.0001, p < 0.0001, p = 0.002, respectively). Women in the third tertile (those with the highest number of years of estrogen exposure) had the lowest age-adjusted prevalence and severity of CAD (p = 0.006, p = 0.014, and p = 0.016 for CAD defined as > 70% stenosis, > 50% stenosis, or as a severity score, respectively). These data indicate that women with the highest number of years of sustained estrogen exposure have a lower prevalence and severity of obstructive CAD. When the data were adjusted for the duration of HT exposure, the significance disappeared for all outcomes [1].

Comment

The WISE data do not show a correlation between duration of HT and atherosclerosis in individual participants. There may be significant inhibitions of atherosclerosis when estrogen is initiated at the time of menopause. The data from other observational studies find a decreased incidence of CAD in HT users who initiate therapy at menopause [6]. The Women’s Health Initiative has recently confirmed that there is no increase in the incidence of CAD events in younger women between the ages of 50 and 59 years who initiate HT after the menopause [7]. These data support the timing hypothesis that early use of HT prevents or retards atherosclerosis [8]. Early use of estrogen after oophorectomy in the Cynomologous macaque and women retards the development of atherosclerosis, but has no effect when hormones are started later after the surgical menopause [3, 9].

Increased serum levels of free estradiol, sex hormone binding globulin and free testosterone in postmenopausal women using exogenous estradiol have been associated with a significant reduction in the progression of carotid intima media thickness, a surrogate marker for atherosclerosis [10]. These unique findings could explain why, in some women, the use of exogenous estrogen for HT has a significant impact on atherosclerosis progression, while in others it does not, and offer an explanation for the diversity of the cardiac event outcome in clinical trials [10]. The mechanism(s) whereby estrogen prevents CAD in the postmenopausal woman continues to be unresolved and requires further investigation. The heterogeneity of the population presenting for treatment indicates the need for an informed decision by the clinician regarding who should receive hormone therapy.